Compact laser sensors and monitoring systems including such sensors

Abstract

Improved laser sensors ( 10 ) employing doped laser crystals ( 24 ) for transducing output proportional to forces impinging upon the sensors. The disclosed sensors are compact, low powered and may be constructed relatively inexpensively from readily available materials. The disclosed sensors eliminate the need for costly, optical power-sapping fiber connections at the laser crystals. According to certain embodiments, the disclosed sensors are configured for local recovery of output signals using conventional digital telemetry. According to other embodiments, the sensors generate output through a dense wavelength division multiplexing (DWDM) laser ( 28 ), thereby allowing remote recovery without the need for frequency division multiplexing and issues involved with preloading the sensors to produce beat frequencies in unique bands.

We claim: 
     
       1. A laser sensor comprising:
 a doped lasing crystal arranged to generate a light at two different frequencies with two orthogonal polarizations, said light exhibiting a beat frequency between said two different frequencies which varies in accordance with a force incident upon the lasing crystal; 
 a pump diode generating an excitation light to drive said lasing crystal, said pump diode adjacent to and directly coupled to a first end of said lasing crystal; and 
 a photodetector directly coupled to a second end of said lasing crystal. 
 
     
     
       2. The laser sensor of  claim 1 , further comprising an FM receiver capable of reading output current from said photodiode. 
     
     
       3. The laser sensor of  claim 2 , further comprising a baseboard including a circuit, wherein said lasing crystal, said pump diode, said photodetector and said FM receiver are attached to said baseboard and form part of said circuit. 
     
     
       4. The laser sensor of  claim 3 , wherein said circuit comprises a capacitor attached to said baseboard and arranged to store power to be supplied to said circuit. 
     
     
       5. The laser sensor of  claim 4 , wherein said circuit further comprises a DC power regulator and trickle charger unit arranged to charge said capacitor and regulate said power. 
     
     
       6. The laser sensor of  claim 1 , comprising:
 a dense wavelength division multiplexing laser in communication with said photodetector, said dense wavelength division multiplexing laser generating an output modulated by output current from said photodetector and exhibiting frequency shifts proportional to said force; and 
 a fiber optic cable connected to said dense wavelength division multiplexing laser for transmitting said output. 
 
     
     
       7. The laser sensor of  claim 6 , comprising at least one fiber connector connected to said fiber optic cable, said at least one fiber connector being arranged for connection to a fiber optic transmission line. 
     
     
       8. The laser sensor of  claim 6 , comprising a baseboard including a circuit, wherein said lasing crystal, said pump diode, said photodetector and said dense wavelength division multiplexing laser are attached to said baseboard and form part of said circuit. 
     
     
       9. The laser sensor of  claim 8 , wherein said circuit comprises a capacitor attached to said baseboard and arranged to store power to be supplied to said circuit. 
     
     
       10. The laser sensor of  claim 9 , wherein said integrated circuit comprises a DC power regulator and trickle charger arranged to charge said capacitor and regulate said power. 
     
     
       11. The laser sensor of  claim 7 , wherein said at least one fiber optic connector comprises:
 an input connector connected to an input end of said fiber optic cable; and 
 an output connector connected to an output end of said fiber optic cable. 
 
     
     
       12. The laser sensor of  claim 6 , wherein said dense wavelength division multiplexing laser is a 1550 nm ITU grid telemetry laser. 
     
     
       13. A seismic or sonar monitoring system comprising:
 a fiber optic transmission line; 
 a seismic or sonar sensor array comprising at least two laser sensors, 
 wherein each of said at least two laser sensors comprises: 
 a doped lasing crystal arranged to generate a light at two different frequencies with two orthogonal polarizations, said light exhibiting a beat frequency between said two different frequencies which varies in accordance with a force incident upon the lasing crystal; 
 a pump diode generating an excitation light to drive said lasing crystal, said pump diode adjacent to and directly coupled to a first end of said lasing crystal; 
 a photodetector directly coupled to a second end of said lasing crystal; 
 a dense wavelength division multiplexing laser in communication with said photodetector, said dense wavelength division multiplexing laser generating an output modulated by output current from said photodetector and exhibiting frequency shifts proportional to said force; and 
 a fiber optic cable connected to said dense wavelength division multiplexing laser for transmitting said output, wherein said fiber optic cable is in communication with said fiber optic transmission line; 
 a receiving unit arranged to process said output, said receiving unit comprising: 
 an optical demultiplexer connected to said fiber optic transmission line to demultiplex output light from said at least two laser sensors and to produce demultiplexed outputs; and 
 optical receivers in communication with said optical demultiplexer and arranged to process said demultiplexed outputs from said optical demultiplexer, 
 wherein each of said optical receivers includes a photodiode for converting light into an electrical signal and an analog-to-digital converter for converting an output of said photodiode to digital data. 
 
     
     
       14. The seismic monitoring system of  claim 13 , wherein each of said at least two laser sensors comprises a baseboard including a circuit, wherein said lasing crystal, said pump diode, said photodetector and said dense wavelength division multiplexing laser are attached to said baseboard and form part of said circuit. 
     
     
       15. The seismic monitoring system of  claim 14 , comprising a PZT fiber extending between adjacent laser sensors among said at least two laser sensors, wherein said PZT fiber is arranged to generate power from vibration and or tension of the PZT fiber, and wherein said integrated circuit comprises a capacitor attached to said baseboard and arranged to store said power for powering said circuit. 
     
     
       16. The seismic or sonar monitoring system of  claim 15 , comprising a strength member tension limiter extending between said adjacent laser sensors. 
     
     
       17. The seismic or sonar monitoring system of  claim 15 , wherein said circuit comprises a DC power regulator and trickle charger arranged to charge said capacitor and regulate said power. 
     
     
       18. The seismic or sonar monitoring system of  claim 13 , wherein each of said at least two laser sensors comprises at least one fiber connector connecting said fiber optic cable to said fiber optic transmission line. 
     
     
       19. The seismic or sonar monitoring system of  claim 13 , wherein one or more of said at least two laser sensors comprises:
 an input fiber connector connected to an input end of said fiber optic cable and a downstream portion of said fiber optic transmission line; and 
 an output fiber connector connected to an output end of said fiber optic cable and an upstream portion of said fiber optic transmission line. 
 
     
     
       20. The seismic or sonar monitoring system of  claim 13 , wherein said dense wavelength division multiplexing laser is a 1550 nm ITU grid telemetry laser. 
     
     
       21. The seismic or sonar monitoring system of  claim 13 , comprising a power supply for powering said at least two laser sensors, wherein said power is located remotely from said at least two laser sensors. 
     
     
       22. The seismic or sonar monitoring system of  claim 13 , wherein said receiving unit is located at a dry side of said monitoring system and wherein said sensor array is located at a wet side of said monitoring system. 
     
     
       23. The laser sensor of  claim 1  wherein said directly coupled pump diode is coupled to said lasing crystal by a direct butt coupling integrated-optic. 
     
     
       24. The laser sensor of  claim 1  wherein said directly coupled photodetector is coupled to said lasing crystal by a direct butt coupling integrated-optic. 
     
     
       25. The laser sensor of  claim 1  wherein said directly coupled pump diode is coupled to said lasing crystal by a direct butt coupling integrated-optic and said directly coupled photodetector is coupled to said lasing crystal by a direct butt coupling integrated-optic. 
     
     
       26. The monitoring system of  claim 13  wherein said directly coupled pump diode is coupled to said lasing crystal by a direct butt coupling integrated-optic. 
     
     
       27. The monitoring system of  claim 13  wherein said directly coupled photodetector is coupled to said lasing crystal by a direct butt coupling integrated-optic. 
     
     
       28. The monitoring system of  claim 13  wherein said directly coupled pump diode is coupled to said lasing crystal by a direct butt coupling integrated-optic and said directly coupled photodetector is coupled to said lasing crystal by a direct butt coupling integrated-optic.